2.5. Creating Control Groups

Use the cgcreate command to create cgroups. The syntax for cgcreate is:

cgcreate -tuid:gid-auid:gid -g subsystems:path

where:

-t (optional) — specifies a user (by user ID, uid) and a group (by group ID, gid) to own the tasks pseudo-file for this cgroup. This user can add tasks to the cgroup.

Removing tasks

Note that the only way to remove a task from a cgroup is to move it to a different cgroup. To move a task, the user must have write access to the destination cgroup; write access to the source cgroup is unimportant.

-a (optional) — specifies a user (by user ID, uid) and a group (by group ID, gid) to own all pseudo-files other than tasks for this cgroup. This user can modify the access that the tasks in this cgroup have to system resources.

-g — specifies the hierarchy in which the cgroup should be created, as a comma-separated list of the subsystems associated with those hierarchies. If the subsystems in this list are in different hierarchies, the group is created in each of these hierarchies. The list of hierarchies is followed by a colon and the path to the child group relative to the hierarchy. Do not include the hierarchy mount point in the path.

For example, the cgroup located in the directory /cgroup/cpu_and_mem/lab1/ is called just lab1 — its path is already uniquely determined because there is at most one hierarchy for a given subsystem. Note also that the group is controlled by all the subsystems that exist in the hierarchies in which the cgroup is created, even though these subsystems have not been specified in the cgcreate command — refer to Example 2.5, “cgcreate usage”.

Because all cgroups in the same hierarchy have the same controllers, the child group has the same controllers as its parent.

Example 2.5. cgcreate usage

Consider a system where the cpu and memory subsystems are mounted together in the cpu_and_mem hierarchy, and the net_cls controller is mounted in a separate hierarchy called net. We now run:

~]# cgcreate -g cpu,net_cls:/test-subgroup

The cgcreate command creates two groups named test-subgroup, one in the cpu_and_mem hierarchy and one in the net hierarchy. The test-subgroup group in the cpu_and_mem hierarchy is controlled by the memory subsystem, even though we did not specify it in the cgcreate command.